3 Biology -- Plant Hormones

Describe the structure and mode of action of cytokinins.

1 Answers

^{Kinetin zeatin}

Structure:- Cytokinins are basic in nature. They are either aminopurine or phenyl urea derivatives. They include kinetin and zeatin. They are found in coconut milk, corn endosperm and pears.

Mode of action in cytokinin

1. Control of Transcription and Translation:- It influence nucleic acid metabolism and also helps in transcription and translation.

2. Enzymes and Metabolism:- It increases the activity of respiration as an enzyme. Cytokinin induces the formation of tyramine methyltransferase which catalyses thiamine synthesis. It may be substituted for Glyceric acid in the induction of α-amylase in wheat seeds.

3. The Richmond-Lang Effect:- It suggested that cytokinins play an active role in senescence retardation in detached leaves. The mechanism is based on the postponement of the disappearance of chlorophyll and the degradation of proteins through the activity of the corresponding hydrolases which normally accompany the senescence process. The primary function of cytokinin in this respect is to increase the amino acid accumulation and to increase or retain the protein content.

4. Identification of Cytokinin Receptors:- It contains intracellular receptors which receives information. The receptors are present in cytoplasmic cytokinin-binding sites.

5.Role of Calcium as a Second Messenger in Cytokinin Signal Transduction:- Calcium acts as a second messenger in many signal transduction pathways in plants and animals. It acts through the regulatory protein, calmodulin (CaM), having four high affinity calcium binding sites.Calmodulin itself is inactive as a regulator, but the CaM-Ca complex can bind and activate several enzymes designated CaM-regulated protein kinases. Another group of protein kinases known as Calcium-dependent protein kinases (CDPKs) have calmodulin as an integral part of their structure and their activity is influenced by calcium binding.

6. Cytokinin and Auxin Regulate Plant Cell Cycle:- Both auxin and cytokinins are involved in the regulation of cell cycle by controlling the activity of cyclin-dependent kinases.

If you touch the leaves of Mimosa pudica, it folds and wilts. What kind of movement is this?

This is seismonastic movement. Here, the plant respond to diffused stimulus i.e. our touch or shock .

What is the term for the sleep movement of leaves of leguminous plants?

The term is Nyctinastic movement. It is induced response to diffused stimulus i.e. light or temperature.

Which plant hormone is used to manipulate and stimulate the maturation of sugarcane crop?

Ethylene, the ripening hormone in plants helps in maturation of sugarcane crops by increasing the storage of sucrose in plants.

What are the functions of Auxins in plant growth?

Auxins are one of the most important plant hormones. Theseplant hormones aregenerally produced at the tips of stems and roots. In all vascular plants, auxins play a vital role in:

Cell division.
Plant propagation.
Promoting flowering in plants.
Initiation of roots and stem cuttings.
Prevent premature dropping of fruits and leaves.

Where are plant hormones formed? How are the hormones passed to the specific site of activity?

The plant hormonesare produced by several tissues like the root tips, shoot tips, leaves, meristematic tissues, and apical buds, etc. The presence of vascular tissues like phloem and xylem help in the translocation of hormones to sites of activity.

Describe the physiological effects of auxins.

Auxin is the plant hormone which plays important physiological roles in cell elongation, apical dominance, parthenocarpy etc. It plays an important role in plant life cycles and is essential for plant’s body development.

The physiological effects of auxins are:-

1. Cell elongation :Cell elongation is the main function of auxins and these are well known to promote elongation of stem and coleoptiles. It also promotes the growth of the elongation of cells behind the apical meristem. Where the...

What do your mean by apical dominance?

Apical dominance means that the growing apex of aplant controls the quiescence of buds sitting in lower positions along a shoot.

Where in plants are the below hormones manufactured?a) IAAB) Gibberellinsc) Cytokinins

a) Apical buds and shoot tips

b) Young leaves and root tips

c) Root tips (meristematic zones).

List out the Factors Affecting Plant Growth?

The important factors affecting the growth of plants include:

Temperature.
Light.
Water.
Soil Nutrients.
Plant Growth Regulators

Several variations of wheat are cultivated in autumn and harvested in the next midsummer.a) Give reasonb) What is the flowering in lower temperatures referred to as?c) Name the plant hormone that c...

If planted in spring, winter varieties do not flower or generate mature grains in a span of the flowering season, hence they are cultivated in autumn. Over winter, they sprout and come out as tiny seedlings, resuming growth in the spring and are collected in mid-summer.

b)Vernalisation.

c)Gibberellin.

Write the physiological effects of gibberellins in plant growth.

Physiological effects of gibberellins are:-

1. Elongation of intact stems:

Many plants respond to application of GA by a marked increase in stem length; the effect is primarily one of internode elongation.

2. Dwarf shoots:

Besides general increase in stem length, gibberellins specifically induce internodal growth in some genetically dwarf varieties of plants like Pea and Maize. It appears that dwarf- ness of such varieties is due to internal deficiency of gibberellins.

3. Bolting:

Gibberellins...

Definition of cytokinins and kinetins.

Cytokinins are mild base growth hormones that promotes cell division.It was discovered by Miler et. Al.(1955).

It was later called kinetin.

Kinetin is an active ingredient obtained from coconut milk and yeast DNA.

Physiological effects of cytokinins.

1. Promotion of cell division: The major physiological role of naturally occurring cytokinins isto promote cell division. It is now well established that these are true cell division factors in anumber of lower and higher plants. In the presence of auxins, nearly all cytokinins stimulate celldivision and subsequent callus growth in the parenchymatous cells of several plants.

2. Cell enlargement: The cytokinins can also induce cell enlargement like auxins andgibberellins. This effect of cell...

What is plant hormone?In how many types is it categorised and what are they?

Plant hormones are the organic substances produced in one part of plants which is translocated to another part for regulating one or more physiological reactions even in low concentration.They are also known as phytohormones.They can have promoting or inhibiting effect on a process.

They have been categorised into five types. They are

Auxin
Gibberellins
Cytokinin
Ethylene
Abscissic acid(ABA)

List the effects of auxins and gibberellins on plant growth.

Auxin and gibberellins are generally growth phytohormones. Some major effects of auxin on growth of plants are as follows:

1. Cell elongation:- Cell elongation is the most important function of auxin especially at the region of shoots and root tip behind the apical meristem. Cell enlargement is caused by the solubilisation of carbohydrates, loosening of wall of microfibril and increase permeability and respiration.

2. Root formation:- Auxin promotes root formation in cutting ends of shoots.

3....

Describe the structure and physiological effects of gibberellins.

^{A. Gibbane ring}

^{B. Gibberellin}

Structure of gibberellin:- chemically, gibberellins belong to a large family of diterpene acid which have a comment skeleton called Gibbane ring. More than 100 gibberellins have been identified but gibbane is common in all gibberellins. They only differ in minute structure such as number and position of -OH, CH₃and -COOH groups at different C atoms of gibbane ring.

Gibberellins are acidic in nature and induce growth of the plants. Some major...

Describe how auxins are responsible for bending of the shoots toward the sources of light.

Plants move or bend towards light due to the growth and elongation of the cells. When plants' shoot are exposed to shady region and light is coming from one direction, auxin is synthesized at shady region. Auxin induces the cells to grow longer on the side of the parts which are away from the light and the growth of cells elongate the shoot towards light.

The presence of auxin in shady part induces cell growth causing the particular part bend towards the light. In this way, auxin is...

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